Unless otherwise indicated herein, the description provided in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
A typical cellular wireless network includes a number of base stations (BSs) each radiating to define a respective coverage area in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In particular, each coverage area may operate on one or more carriers each defining a respective frequency bandwidth of coverage. In turn, each base station (BS) may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a BS and may thereby communicate via the BS with various remote network entities or with other UEs served by the BS.
Further, a cellular wireless network may operate in accordance with a particular air interface protocol (radio access technology), with communications from the BSs to UEs defining a downlink or forward link and communications from the UEs to the BSs defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between coverage areas, and other functions related to air interface communication.
In practice, BSs in a cellular wireless network can be physically arranged in various ways. For instance, BSs may be co-located with each other by having their antenna structures at largely the same geographic location (within a defined tolerance, for instance). By way of example, a single cell site could be arranged to define two BSs with separate antenna structures on a common antenna tower or other base structure. And in another example, a single physical BS (possibly with a single antenna structure) that provides service separately on first and second carriers could be considered to define the two separate BSs, one operating on the first carrier and the other operating on the second carrier. Alternatively, BSs in a cellular wireless network can be distributed at some distance from each other. In particular, the antenna structure of a given BS may be located at a geographic location that is at some non-zero distance from the antenna structure of another BS.
With these arrangements, the BSs of a wireless service provider's network would ideally provide seamless coverage throughout a market area, so that UEs being served by the system could move from coverage area to coverage area without losing connectivity. In practice, however, it may not be possible to operate a sufficient number of BSs or to position the BSs in locations necessary to provide seamless coverage. As a result, there may be holes in coverage.
One way to help to resolve this problem is to operate a relay node (RN) that extends the range of a BS's coverage area so as to partially or completely fill a coverage hole. Such an RN may be configured with a wireless relay backhaul air interface (e.g., including a radio resource control (RRC) connection) for communicating with and being served by the BS in much the same way that a UE does, and a wireless relay access interface for communicating with and serving one or more UEs in much the same way that a BS does. Further, the RN may include control logic for actively bridging the backhaul communications with the access communications. The RN may thus receive and recover downlink communications from the donor BS and may transmit those communications to the UEs served by the RN, and may likewise receive and recover uplink communications from UEs served by the RN and may transmit those communications to the BS. Consequently, a wireless service provider may conveniently employ such RNs throughout a region to help efficiently fill coverage holes and improve service quality.
When an RN is being served by a BS over a relay backhaul air interface, the RN may be configured to detect one or more threshold errors in communication on the relay backhaul air interface and to respond to such a threshold error in communication by spending a particular time period trying to overcome the threshold error in communication.
By way of example, the RN may detect a threshold problem with the relay backhaul air interface, such as by detecting a threshold number of instances in which the RN is unable to decode data received by the RN from the serving BS over the relay backhaul air interface for example. And in response to detecting the threshold problem, the RN may start a timer that runs for a timer duration, which according to one or more industry standards may be referred to as a T310 timer. While the T310 timer is running, the RN may undergo a phase (which, for simplicity, could be referred to as a “problem recovery” phase) during which the RN checks whether or not the threshold problem is improving or has otherwise been resolved. If the RN determines that the threshold problem is improving or has otherwise been resolved before expiration of the T310 timer duration (e.g., the RN detects a threshold number of instances in which the RN was able to decode data received from the serving BS), then the RN may responsively stop the T310 timer before expiration of the T310 timer duration and may then resume normal operation while continuing to be served by the BS.
As another example, the RN may detect expiration of the T310 as a further threshold error in communication (and perhaps as an indication that the threshold problem has not improved or otherwise been resolved before expiration of the T310 timer). And in response to expiration of the T310 timer, the RN may responsively start another timer that could be referred to as a T311 timer according to one or more industry standards and that runs for a T311 timer duration (which could be the same as or different from the T310 timer duration).
Upon starting the T311 timer, the RN may initiate an RRC connection re-establishment procedure to re-establish the RRC connection while the RN remains RRC connected and thus without the RN having to transition to an RRC idle mode. As part of the RRC connection re-establishment procedure, the RN may send an RRC connection re-establishment request message respectively to each of one or more target BSs, such as to one or more BSs found on a BS neighbor list stored by the RN (e.g., perhaps including the serving BS itself). In doing so, the RN could transmit such a request to the serving BS over the RRC connection and to a BS other than the serving BS over a physical uplink control channel (PUCCH) that the other BS may use to monitor for such request messages.
Any BS that receives an RRC connection re-establishment request message from the RN may respond with an RRC connection re-establishment response, which may either specify acceptance of the re-establishment request or specify rejection of the re-establishment request (e.g., due to the BS being unable to obtain sufficient information about the RN). In some cases, however, one or more BSs may not respond due to such BSs not successfully receiving the request message and/or for other reasons. Nonetheless, the RN may be configured to take certain action depending on whether and/or how one or more BSs respond to the transmitted request.
In particular, if the RN receives from a BS an RRC connection re-establishment response message accepting the RN's RRC connection re-establishment request before expiration of the T311 timer, then the RN may perhaps engage in control signaling with the responding BS and may then resume normal operation while being be served over an RRC connection by that responding BS. However, if the RN detects expiration of the T311 timer and has not received from any BS an RRC connection re-establishment response message accepting the RN's RRC connection re-establishment request, then the RN may respond to expiration of the T311 timer duration by transitioning from operating in an RRC connected mode to operating in an RRC idle mode. While the RN then operates in the RRC idle mode, the RN may scan for possible coverage and, once the RN finds coverage, the RN may engage in attach and/or other signaling to establish a new RRC connection with a target BS defining the coverage area, which may be the same BS on which the RN was already being served or may be another BS other than the BS on which the RN was already being served.